Removal Mechanisms and Microstructure Characteristics of Laser Paint Stripping on Aircraft Skin Surface

As a non-contact and non-destructive technology, laser cleaning provides an alternative method for the paint stripping of aircraft skins. Herein, the particular multi-layer paint on the aluminum alloy aircraft skin surface was stripped by adjusting laser parameters. Beyond expectation, multi-layer paint led to a highly complex surface as opposed to the ordinary single-layer paint after laser cleaning. The surface morphology, chemical compositions, and surface functional groups of the samples were analyzed, and the successful depaint parameters were found in this experiment with damage free of the aluminum substrate, i.e., laser energy density of 5.09 J/cm2 and scanning speed of 700 mm/s. More importantly, this paper revealed that the mechanisms of laser paint stripping from Al alloy aircraft skin are thermal decomposition, evaporation, and spallation. After laser cleaning, the surface nanoindentation hardness with paint completely stripped and undamaged was increased by 3.587% relative to that of the conventional mechanical lapping sample. The improvement of nanoindentation hardness was also confirmed by the microstructure characterized with electron backscatter diffraction (EBSD) in which plastic deformation led to strain hardening of the substrate surface. This study lays a solid foundation for large-scale, high-efficiency, and low-pollution removal of more complex paint layers on aircraft surfaces in the future.